The invention generally relates to circuit boards and, more particularly, the invention relates to reducing high frequency noise produced by data signals transmitted through circuit traces on a circuit board.
Circuit boards commonly are constructed with multiple layers that each have a specific function. For example, one layer may be utilized for powering electronics, another for high speed memory circuitry (e.g., memory that operates between about 66 and 300 megahertz), and another for grounding purposes. Each of these layers typically is separated by an insulator, such as fiberglass, to prevent undesired electrical coupling between the adjacent layers. When necessary, inter-layer conductors, known in the art as xe2x80x9cviasxe2x80x9d, can be utilized to electrically couple circuit elements on one layer with circuit elements on other layers.
Since high speed memory circuitry operates synchronously (i.e., at specific frequencies), data signals transmitted on a high speed memory layer commonly emit high frequency noise. Undesirably, high frequency noise often shunts to ground through other circuits that are located in a relatively close proximity to such circuitry (e.g., circuits on an adjacent layer). Receipt of such noise consequently can corrupt signals transmitted by circuits receiving the noise, thus degrading the operation of the entire circuit board.
In accordance with one aspect of the invention, a multilayer circuit board includes a set of conductors that are coupled with ground to remove undesired high frequency noise. To that end, the multilayer circuit board includes a first layer having a circuit trace in the form of a serpentine, a ground layer set to a reference potential, and the set of conductors noted above. Each of the conductors extends from the first layer to the ground layer from within an interior portion of the serpentine. The set of conductors electrically contact the ground layer.
In preferred embodiments, the reference potential is zero volts, such as a ground potential. The set of conductors may be arranged to form a bandpass filter that filters signals transmitted at a prescribed frequency through the serpentine. The bandpass filter has a minimum and maximum frequency, where the minimum frequency is greater than the prescribed frequency. In preferred embodiments, the minimum frequency is a harmonic of the prescribed frequency.
The first layer and ground layer may be substantially parallel. The circuit board also may include a second layer that also is set to the reference potential. The first layer thus is positioned between the second layer and the ground layer. In such embodiment, each conductor in the set of conductors has a ground end coupled with the ground layer, and a second layer end electrically coupled with the second layer. The circuit board may include other electronic modules, such as a modem. The interior of the serpentine is bounded by the circuit trace and may include an insulator. An insulator may be positioned between the first layer and the ground layer.
In accordance with another aspect of the invention, a multilayer circuit board includes a first layer having a circuit trace forming a serpentine that defines an interior bounded by the circuit trace, a ground layer set to a reference potential, and a set of conductors extending from the interior of the serpentine to the ground layer. The circuit trace includes an input for receiving a signal that is transmitted at a prescribed frequency. The set of conductors is arranged to remove noise from the signal transmitted through the circuit trace. The noise that is removed has a frequency that is greater than the prescribed frequency of the signal.
The set of conductors preferably are arranged to form a bandpass filter for filtering noise from the signal. The bandpass filter has a minimum frequency that is greater than the prescribed frequency. The minimum frequency preferably is a harmonic of the prescribed frequency.
In accordance with other aspects of the invention, a method of manufacturing a multilayer circuit board couples a ground layer to a first layer, sets the ground layer to a grounding reference potential, and forms a circuit trace on the first layer in the form of a serpentine having an interior. The method also extends a set of conductors from the interior of the serpentine, and electrically couples them with the ground layer.
In preferred embodiments, an insulator is coupled between the ground layer and the first layer. The set of conductors may be spaced within the interior of the serpentine to form a bandpass filter that filters data signals transmitted through the circuit trace.